Along with the high integration and miniaturization of semiconductor devices typified by DRAM (Dynamic Random Access Memory), materials for metal films and metal oxide films constituting these devices need to be changed.
Especially the improvement of a conductive metal film for use in multi-layer wiring in semiconductor devices is desired, and a shift to copper wiring having high conductivity is now under way. Although a low-dielectric material (low-k material) is used as an interlayer insulating film material for multi-layer wiring in order to enhance the conductivity of this copper wiring, there occurs a problem that an oxygen atom contained in the low-k material is easily introduced into the copper wiring to reduce its conductivity. Therefore, to prevent the movement of oxygen from the low-k material, a technology for forming a barrier film between the low-k material and the copper wring is now under study. As a material for this barrier film, which hardly takes in oxygen from a dielectric layer and can be easily processed by dry etching, a metal ruthenium film is attracting attention. Further, metal ruthenium is attracting attention to meet the requirements for the above barrier film and a film grown by plating at the same time in the Damascene film growth method for burying the above copper wring by plating (refer to Electronic Materials, November issue, pp. 47-49, November, 2003, and Jpn. J. Appl. Phys., Vol. 43, No. 6A, pp. 3315-3319, 2004).
Even in a capacitor for semiconductor devices, a metal ruthenium film is also attracting attention for its high oxidation resistance and high conductivity as an electrode material having a high dielectric constant such as alumina, tantalum pentaoxide, hafnium oxide or barium titanate•strontium (BST) (refer to JP-A 2003-100909).
Although sputtering has often been used for the formation of the above metal ruthenium film, a chemical vapor deposition method is now under study to produce a finer structure, reduce the thickness of the film and enable its mass-production (refer to JP-A2003-318258, JP-A2002-161367 and JP-A 2002-523634).
However, a metal film formed by the chemical vapor deposition method generally has bad surface morphology such as the sparse assembly state of fine crystals, and studies on the use of bis(dipivaloylmethanato)ruthenium, ruthenocene and bis(alkylcyclopentadienyl)ruthenium as materials for chemical vapor deposition are under way as means of solving the above morphology problem (refer to JP-A 06-283438, JP-A 11-35589 and JP-A 2002-114795).
When these materials for chemical vapor deposition are used in the production process, they must have high storage stability in order to stabilize the production conditions. However, existing ruthenocene and bis(alkylcyclopentadienyl)ruthenium are oxidized and deteriorated by the inclusion of air or the like in a short period of time with the result that the conductivity of the formed ruthenium film is reduced. Therefore, they have problems with storage stability and stable handling properties in air. Further, when bis(dipivaloylmethanato) ruthenium having high storage stability is used as a material for chemical vapor deposition, the formed ruthenium film contains large amounts of impurities, and a high-quality ruthenium film is not obtained. Ruthenium compounds having a carbonyl compound or a diene compound as a ligand and compounds having a ruthenium(II) valence have been studied as means of solving the above problems (refer to JP-A 2002-212112, JP-A 2003-342286 and JP-A 2006-241557). However, it is difficult to achieve storage stability for the compounds and reduce the total content of impurities remaining in the formed ruthenium film at the same time. Therefore, there still remain problems to be solved.